A beloved romance novel, the main thread of The Notebook tells the story of Noah and Allie, who fall in love just before the outbreak of WWII. Although the two are deeply in love, Allie's respectable family does not approve of Noah, who comes from a poor family. Their differences and the oncoming war separate them for more than a decade, but they are eventually reunited. A parallel storyline takes place in the present day, where an elderly Noah is reading the story of their romance to Allie, who has Alzheimer's.
Boasting the largest collection of book summaries, BookRags is the best option for titles you can't find elsewhere. They offer all of the basics (quotes, chapter summary, characters, historical context, literary criticism) but also walk through a few major topics that recur throughout the book, which can be particularly useful for essay writing.
The original provider of professionally-written study guides, Cliffs Notes were available in print form before the Internet even existed. Their content is very comprehensive and includes an analysis of characters, detailed chapter by chapter summaries, critical essays, essay topics, and many other sections.
Their book summaries aren't as good as other providers, but PinkMonkey often has interesting insights that aren't mentioned elsewhere on the Internet. For example, they go over literary elements (like setting, conflict, and mood), compare and contrast, and symbolism/motifs. It's a good site if you want to find a unique fact or angle that other students don't know about.